可編程邏輯系統通常部署在可能存在噪聲的應用中。這種噪聲會影響可編程邏輯設計接收的信號。例如，它可能會導致信號故障或跳動，如果處理不當，可能會導致設計和操作出現問題。

毛刺的持續時間是隨機的，并且與時鐘沿不同步。因此，它們可能會導致下游信息損壞。

處理此問題的最常見方法是使用毛刺濾波器來濾除毛刺和反彈。

毛刺濾波器核心是使用長度可變的移位寄存器，噪聲信號被放到寄存器中，直到移位寄存器的所有值都一致。此時，信號可以視為穩定。當然，我們必須確定潛在毛刺和反彈可能持續多長時間，以確保時鐘周期的寄存器大小正確。這就是為什么我們的毛刺濾波器需要非常靈活，并且需要確保其大小能夠適合每個應用程序的要求。

濾波器應該能夠接收噪聲輸入并濾除持續時間為多個時鐘脈沖的毛刺。

libraryieee;
useieee.std_logic_1164.all;
useieee.numeric_std.all;

entityglitch_filteris
generic(
G_FILER_LEN:integer:=8
);
port(
i_clk:instd_ulogic;
i_noisy:instd_ulogic;
o_clean:outstd_ulogic
);
endglitch_filter;

architecturebehaviourofglitch_filteris

signals_delay_line:std_ulogic_vector(G_FILER_LEN-1downto0);
signals_delay_and:std_ulogic;
signals_delay_nor:std_ulogic;
signals_output_clean:std_ulogic;

begin

o_clean<=?s_output_clean;

????--Delay?disctete?using?delay?line
????synchroniser_process?:?process?(i_clk)?begin
????????if?rising_edge(i_clk)?then
????????????s_delay_line?<=?s_delay_line(G_FILER_LEN?-?2?downto?0)?&?
????????????????????????????i_noisy;
????????end?if;
????end?process;

????--Generate?AND?and?NOR?of?delay?line?bits
????s_delay_and?<=?'1'?when?to_01(s_delay_line)?=?
????????????????????????????(s_delay_line'range?=>'1')else'0';
s_delay_nor<=?'1'?when?to_01(s_delay_line)?=?
????????????????????????????(s_delay_line'range?=>'0')else'0';

--Setdiscretebasedondelayline
output_process:process(i_clk)begin
ifrising_edge(i_clk)then
ifs_delay_nor='1'then
s_output_clean<=?'0';
????????????elsif?s_delay_and?=?'1'?then
????????????????s_output_clean?<=?'1';
????????????end?if;
????????end?if;
????end?process;

end?behaviour;

為了測試這個模塊，創建一個簡單的測試文件，它將隨機數量的毛刺注入信號中。在信號改變狀態后，許多隨機毛刺被輸入到信號中。如果濾波器運行正常，則這些毛刺將在毛刺濾波器輸出干凈的信號。

libraryieee;
useieee.std_logic_1164.all;
useieee.numeric_std.all;
useieee.math_real.all;

entityglitch_filter_tbis
end;

architecturebenchofglitch_filter_tbis

componentglitch_filter
generic(
G_FILER_LEN:integer
);
port(
i_clk:instd_ulogic;
i_noisy:instd_ulogic;
o_clean:outstd_ulogic
);
endcomponent;

--Clockperiod
constantclk_period:time:=10ns;
--Generics
constantG_FILER_LEN:integer:=8;

--Ports
signali_clk:std_ulogic:='0';
signali_noisy:std_ulogic;
signalo_clean:std_ulogic;

begin

i_clk<=?not?i_clk?after?(clk_period/2);

??glitch_filter_inst?:?glitch_filter
????generic?map?(
??????G_FILER_LEN?=>G_FILER_LEN
)
portmap(
i_clk=>i_clk,
i_noisy=>i_noisy,
o_clean=>o_clean
);

uut:process

variableglitch_duration:integer;
variableseed1:positive:=1;
variableseed2:positive:=283647823;

impurefunctioninteger_random(min,max:integer)returnintegeris
variablerandom:real;
begin
uniform(seed1,seed2,random);
returninteger(round(random*real(max-min)+real(min)));
endfunction;

begin
i_noisy<=?'0';
????wait?until?rising_edge(i_clk);
????wait?for?G_FILER_LEN?*?clk_period;
????test:?for?i?in?0?to?1?loop
????????i_noisy?<=?'1';
????????wait?until?rising_edge(i_clk);
????????glitch_duration?:=?integer_random(1,5);
????????for?x?in?0?to?glitch_duration?loop
????????????i_noisy?<=?not?i_noisy;
????????????wait?until?rising_edge(i_clk);
????????end?loop;
????????i_noisy?<=?'1';
????????wait?for?20?*?clk_period;
????????report?"loop?high?completed"?severity?note;
????????i_noisy?<=?'0';
????????wait?until?rising_edge(i_clk);
????????glitch_duration?:=?integer_random(1,5);
????????for?x?in?0?to?glitch_duration?loop
????????????i_noisy?<=?not?i_noisy;
????????????wait?until?rising_edge(i_clk);
????????end?loop;
????????i_noisy?<=?'0';
????????wait?for?20?*?clk_period;
????????report?"loop?low?completed"?severity?note;
????end?loop;
????report?"Simulation?complete"?severity?failure;
????
end?process;

end;

運行仿真后顯示在信號狀態改變后隨機數量的脈沖便增加。檢查輸出信號表明濾波器已正確濾除輸入信號中可能存在的毛刺。

正如在一開始所說的，這樣的濾波器對于部署在可能存在電噪聲的環境中非常有用。與 BRAM 上的 EDAC 等其他緩解策略相結合，這是可用于實現設計彈性的關鍵方法之一。

審核編輯：劉清